US5699079A - Restoration filter for truncated pixels - Google Patents

Restoration filter for truncated pixels Download PDF

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Publication number
US5699079A
US5699079A US08/561,584 US56158495A US5699079A US 5699079 A US5699079 A US 5699079A US 56158495 A US56158495 A US 56158495A US 5699079 A US5699079 A US 5699079A
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pixel
displayed
truncated
comparing
bits
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Expired - Lifetime
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US08/561,584
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English (en)
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Carroll Philip Gossett
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Nintendo Co Ltd
RPX Corp
Morgan Stanley and Co LLC
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Silicon Graphics Inc
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Priority to JP8351768A priority patent/JPH1026965A/ja
Priority to EP96308414A priority patent/EP0775983B1/de
Priority to DE69621208T priority patent/DE69621208T2/de
Assigned to SILICON GRAPHICS, INC. reassignment SILICON GRAPHICS, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GOSSETT, CARROL PHILIP
Assigned to SILICON GRAPHICS, INC. reassignment SILICON GRAPHICS, INC. CORRECT CONVEYING PARTY NAME ON REEL 8577 FRAME 0981 Assignors: GOSSETT, CARROLL PHILIP
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Assigned to WELLS FARGO FOOTHILL CAPITAL, INC. reassignment WELLS FARGO FOOTHILL CAPITAL, INC. SECURITY AGREEMENT Assignors: SILICON GRAPHICS, INC. AND SILICON GRAPHICS FEDERAL, INC. (EACH A DELAWARE CORPORATION)
Assigned to GENERAL ELECTRIC CAPITAL CORPORATION reassignment GENERAL ELECTRIC CAPITAL CORPORATION SECURITY INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: SILICON GRAPHICS, INC.
Assigned to MORGAN STANLEY & CO., INCORPORATED reassignment MORGAN STANLEY & CO., INCORPORATED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GENERAL ELECTRIC CAPITAL CORPORATION
Assigned to GRAPHICS PROPERTIES HOLDINGS, INC. reassignment GRAPHICS PROPERTIES HOLDINGS, INC. CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: SILICON GRAPHICS, INC.
Assigned to RPX CORPORATION reassignment RPX CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GRAPHICS PROPERTIES HOLDINGS, INC.
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    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T5/00—Image enhancement or restoration
    • G06T5/20—Image enhancement or restoration using local operators

Definitions

  • This invention relates generally to computer graphics systems, and more specifically to a system and method for restoring bits of pixels prior to display where the original bits of the pixels were truncated.
  • Computer graphics systems in which graphics processors are used to draw images on a display screen are enjoying widespread acceptance in many facets of the current electronics marketplace. This is true for high-end computer graphics workstations as well as mid-range and low-end consumer oriented products.
  • the graphics processor draws, or renders, the image by generating attribute information for each pixel of the display.
  • Each pixel of the display is represented by a plurality of bits. Depending on the display characteristics and the complexity of the graphics system, these bits can represent attributes of the pixel such as color (e.g., red, green and blue bits or a grey scale), transparency or opacity, depth, and other like attributes.
  • cost-benefit tradeoffs that must be performed when specifying a computer graphics system.
  • One such cost-benefit tradeoff is that which exists between the cost of memory and the number of planes provided in the frame buffer (i.e., the number of bits dedicated to each pixel).
  • Systems with more planes i.e., more bits per pixel
  • One way to decrease the number of bits per pixel used is to truncate the bits. That is, the pixels are generated with the full complement of bits, and the low-order bits are truncated prior to storage in the frame buffer. Thus, the image can be rendered with fewer bits per pixel and the size of the frame buffer can be decreased.
  • the 3 least significant bits are truncated.
  • truncation is that the use of too few bits can result in unacceptable artifacts such as quantization (sometimes known as "mach banding") and poor image quality.
  • mach banding quantization
  • dithering is sometimes used to disrupt the regularity of the artifacts, thereby softening the effects of reach banding.
  • dithering is perceived by the eye as noise and can itself be objectionable, especially at low quantities of bits per pixel.
  • the present invention is directed toward a system and method for restoring bits of pixels prior to display where the original bits of the pixels were truncated.
  • the bits removed during truncation are restored.
  • the restoration process is accomplished by comparing each pixel to its neighbors to determine the relative value of each pixel as compared to its neighbors. As a result of this comparison, a restoration value is determined for each pixel. This restoration value is added to the truncated pixel prior to display.
  • the restoration process is executed for each pixel as follows. First, the pixel is shifted. That is, the remaining bits of the pixel are shifted to the left and additional bits are added in the least significant bit positions. These additional bits are referred to as the restoration offset of the pixel. Preferably, these additional bits are zeroes. The entire pixel comprising the shifted truncated portion and the restoration offset is referred to as the truncated shifted pixel, or the restored pixel.
  • the pixel is compared to each neighbor to determine their relative values. For each neighbor that is greater than the pixel in question, the restoration offset is incremented by one. Similarly, for each neighbor that is less than the pixel in question, the restoration offset is decremented by one. In the preferred embodiment, overflow of the restoration offset resulting from the increment/decrement operations is carded over into the truncated and shifted portion of the pixel. In other words, in the preferred embodiment, it is actually the truncated shifted pixel which is incremented or decremented for each neighbor compared.
  • the restored pixel can then be displayed including the original truncated and shifted portion and the determined restoration offset.
  • the number of bits by which the truncated portion is shifted, and hence the number of bits used for the restoration offset is the same as the number of bits which were removed from the pixel during truncation.
  • a restoration offset value By starting with an initial value (such as zero) and incrementing the restoration offset value for each neighbor greater than the pixel to be displayed, and decrementing the restoration offset value for each neighbor that is less than the pixel to be displayed.
  • the restoration offset value is then appended to the truncated portion of the pixel prior to display. Note, however, that this may result in the situation where the restoration value underflows or overflows must be handled, whereas this condition is automatically handled in the embodiment where the truncated portion is shifted and the truncated portion itself is incremented/decremented based on the comparison results.
  • One advantage of the invention is that it allows image data to be stored in a truncated format while minimizing the visible side effects of truncation and dithering.
  • FIG. 1 is a block diagram illustrating a simplified graphics system which forms an example environment of the invention.
  • FIG. 2 is a diagram illustrating a neighborhood of pixels having a central pixel and eight neighbor pixels.
  • FIG. 3 is a diagram illustrating a restored pixel having a truncated portion and a restored portion.
  • FIG. 4 is an operational flow diagram illustrating the operation of the restoration filter according to one embodiment of the invention.
  • the present invention is directed toward a system and method for back-filtering to remove the unwanted side effects of dithering in a computer graphics system.
  • the back filtering is a process of comparing each pixel to its surrounding neighbors and determining a restoration offset for the pixel based on the results of the comparison process.
  • each truncated pixel is shifted left by the number of bits to be restored. This has the effect of appending a series of zeroes to the pixel. This series of appended bits is referred to as the restoration offset of the pixel.
  • the resultant pixel, including the truncated portion and the restoration offset is referred to as the truncated shifted pixel, or the restored pixel.
  • the truncated shifted pixel For each neighbor having a greater value than the pixel in question, the truncated shifted pixel is incremented by one. Similarly, for each neighbor having a value less than the pixel in question, the truncated shifted pixel is decremented by one. The net result of this increment/decrement operation is that a restored value of the restored pixel is computed and the restored pixel can be displayed.
  • FIG. 1 is a block diagram illustrating a basic graphics system 100.
  • the basic graphics system 100 includes a graphics processor 104, a frame buffer 108, a video interface 112 and a display device 116.
  • graphics processor 104 renders the image to be displayed by generating each pixel of the image.
  • Each pixel is comprised of a plurality of bits representing attributes of that pixel such as color or grey scale, transparency, opacity, reflectivity, etc.
  • the pixels generated by graphics processor 104 are stored in frame buffer 108 as they are generated. When the entire frame is generated, the image is transferred from frame buffer 108 to display device 116 via video interface 112.
  • Video interface 112 provides synchronization and timing signals needed to display the image on display device 116.
  • Dithering adds a dither noise to the calculated intensity of the pixels.
  • the amount of dither added to each pixel can be determined with a random process, a pseudo random process or with a calculation based on the coordinate position of the pixel. Adding a dither value to the pixel tends to break up the contours of objects and the overall appearance of the rendered scene is improved.
  • a dither matrix is defined with integers zero through three assigned to matrix positions.
  • An example dither matrix for this case may be: ##EQU1##
  • any of a number of commonly known dither matrices can be employed for the dithering operation.
  • One such matrix is the well known Bayer ordered dither matrix. In the example where 8 bits are being truncated to five, three bits of dither need to be added before truncation. In this case, a four-by-four dither matrix is used with the four-bit values truncated to three bits (by shifting down and dropping the least significant bit).
  • the truncated Bayer matrix is as follows: ##EQU2##
  • the dithering is done in two parts. First, a dither pattern is generated and added to the full complement of bits before truncation. This can be done in the end of the rendering pipeline at the time of rendering just before the image is stored in frame buffer 108. In conventional systems, the stored image is processed and displayed using the truncated format.
  • the restoration filter according to the invention is used to replace the bits of the original image that were removed during truncation. This operation is performed at the time that the image is displayed and, preferably performed by video interface 112.
  • the restoration filter is used to replace the truncated bits for each pixel by comparing the pixel to the immediately adjacent pixels.
  • This section of the patent document describes the restoration filter in terms of an example graphics system having an original complement of eight bits per pixel which has been truncated to five bits per pixel and which is to be restored to the full complement of eight bits per pixel prior to display. After reading this description, it will become apparent to a person skilled in the relevant art how to implement the restoration filter with graphics systems having other bit complements and other levels of truncation.
  • the number of bits in the restoration offset are three, and there are eight neighbors.
  • the value used to increment or decrement the restoration offset is one.
  • alternative embodiments can be implemented.
  • alternative embodiments can be implemented wherein the neighborhood size is larger or smaller.
  • Additional alternatives include embodiments where the increment and/or decrement value is some amount other than one.
  • Still other alternatives encompass a combination of these two variations (i.e., different neighborhood size and a different increment and/or decrement values). Such variations will become obvious to one of ordinary skill in the art after reading the above disclosure.
  • FIG. 2 illustrates a three-by-three block of pixels 200.
  • Center pixel 204 the pixel being restored, is compared to each of its neighboring pixels 208.
  • FIG. 3 illustrates the restored complement of eight bits for a sample pixel having two portions.
  • the first portion is truncated portion 304 which in the example description is a five bit portion.
  • the second portion is the restoration offset portion 308.
  • the least significant bit (LSB) of truncated portion 304 is referred to as LSB 312 and the least significant bit of restoration offset portion 308 is referred to as sub-LSB 316.
  • the restoration according to the invention is based on the assumption that the neighbor pixels 208 were of the same or similar eight-bit-per-component color of the center pixel 204. If this is not the case, the truncation error is probably not noticeable due to the higher contrast real gradient.
  • the restoration filter simply compares each of the eight neighbor pixels 208 with center pixel 204.
  • the manner in which this is accomplished is described with reference to the operational flow diagram illustrated in FIG. 4.
  • the first step is to identify the eight neighboring pixels 208 of the pixel in question (i.e., identify the neighbors of center pixel 204). This is illustrated by box 404 in FIG. 4. Note that where the pixel in question is a corner pixel or a border pixel, it may not have a full complement of eight neighbors 208.
  • the next operation performed by the restoration filter is to shift center pixel 204 up three bits, inserting all zeroes to the three least significant bits.
  • the five bit truncated portion 304 of center pixel 204 is augmented by adding an all zero restored portion 308.
  • This shifting step is illustrated by operation box 408 in FIG. 4. This results in a truncated shifted pixel.
  • the operation continues by comparing center pixel 204 with a neighboring pixel 208 to determine whether the neighboring pixel's five-bit truncated value is greater than or less than the value of truncated portion 304 of center pixel 204. This step of comparing to determine the relative value of center pixel 204 with neighboring pixel 208 is illustrated by decision box 412.
  • truncated portion 304 for the compared neighboring pixel 208 is greater than the value of truncated portion 304 of center pixel 204
  • the truncated shifted center pixel 204 is incremented by one. This is illustrated by operation box 416.
  • the steps of comparing and incrementing or decrementing are repeated for each neighboring pixel 208 as illustrated by decision box 426 and flow line 462.
  • decision box 426 the steps of comparing and incrementing or decrementing are repeated for each neighboring pixel 208 as illustrated by decision box 426 and flow line 462.
  • the operation is complete as illustrated by done block 424. Note that it is possible to do the comparison, increment and decrement operations for each neighbor in parallel.
  • the restoration filter according to the present invention effectively reconstructs the missing bits which were removed during truncation prior to storage into frame buffer 108.
  • the maximum error introduced by the restoration is limited to the restored portion 308. In the case of the eight bit example described above, the maximum error is three bits, or eight levels out of 256. This results in a slight error in steep gradients, which is acceptable.
  • the center pixel 204 is compared to the neighbors and its restored portion 308 incremented or decremented based on the results of the comparison.
  • Alternative embodiments are contemplated wherein other algorithms are used to reconstruct restored portion 308.
  • the restoration filter described above works for any ordered dither pattern, pseudo-random dither pattern and for systems where no dithering is used, it works best where dithering is performed using a matrix that is carefully chosen to match the reconstruction filter. Results achieved using the standard Bayer matrix during the dithering process are passable but result in a visible high-frequency pattern after the restoration filter is applied.
  • the ⁇ magic square ⁇ matrix, described above spreads the error energy more effectively into lower-amplitude, lower-frequency patterns that are frequently less visually objectionable, although which looks better is, to some extent, a function of the image content.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Image Processing (AREA)
  • Editing Of Facsimile Originals (AREA)
  • Facsimile Image Signal Circuits (AREA)
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US08/561,584 1995-11-21 1995-11-21 Restoration filter for truncated pixels Expired - Lifetime US5699079A (en)

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Application Number Priority Date Filing Date Title
US08/561,584 US5699079A (en) 1995-11-21 1995-11-21 Restoration filter for truncated pixels
JP8351768A JPH1026965A (ja) 1995-11-21 1996-11-20 ビット間引きされた画素の復元フィルタ
EP96308414A EP0775983B1 (de) 1995-11-21 1996-11-21 Wiederherstellungsfilter für abgeschnittene Pixel
DE69621208T DE69621208T2 (de) 1995-11-21 1996-11-21 Wiederherstellungsfilter für abgeschnittene Pixel

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Cited By (16)

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Publication number Priority date Publication date Assignee Title
US6088395A (en) * 1997-09-23 2000-07-11 Winbond Electronics Corp. Compressing/decompressing apparatus and method to compress and decompress a video graphics signal
US6104377A (en) * 1996-05-24 2000-08-15 Microsoft Corporation Method and system for displaying an image at a desired level of opacity
WO2003025897A1 (fr) * 2001-09-14 2003-03-27 Nec Corporation Appareils de traitement, emission, reception d'images et procede de traitement d'images
US20030072468A1 (en) * 2000-12-18 2003-04-17 Digimarc Corporation Curve fitting for synchronizing readers of hidden auxiliary data
US20030177359A1 (en) * 2002-01-22 2003-09-18 Bradley Brett A. Adaptive prediction filtering for digital watermarking
US6812939B1 (en) 2000-05-26 2004-11-02 Palm Source, Inc. Method and apparatus for an event based, selectable use of color in a user interface display
US6879721B2 (en) 2001-01-02 2005-04-12 Hewlett-Packard Development Company, L.P. Pixel processing system for image production
US20060008155A1 (en) * 2004-07-07 2006-01-12 Takashi Ishikawa Image processing device
US7075555B1 (en) * 2000-05-26 2006-07-11 Palmsource, Inc. Method and apparatus for using a color table scheme for displaying information on either color or monochrome display
US7081901B1 (en) * 2002-08-29 2006-07-25 National Semiconductor Corporation Display system with framestore and stochastic dithering
US20070279432A1 (en) * 2006-05-31 2007-12-06 Jean Noel Method and Apparatus for Spatial and Temporal Dithering
US7945781B1 (en) 1993-11-18 2011-05-17 Digimarc Corporation Method and systems for inserting watermarks in digital signals
CN101197118B (zh) * 2006-11-22 2012-01-11 瑞萨电子株式会社 用于改进的frc技术的显示设备和控制驱动器
US20130229425A1 (en) * 2012-03-03 2013-09-05 Mstar Semiconductor, Inc. Image processing method and associated apparatus
US20130287101A1 (en) * 2011-10-20 2013-10-31 Thomson Licensing Method and device for encoding a video frame, method and device for decoding a video frame and storage medium
US20150117782A1 (en) * 2013-10-31 2015-04-30 Stmicroelectronics Asia Pacific Pte. Ltd. Banding noise detector for digital images

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JP3308545B2 (ja) * 1996-04-18 2002-07-29 カネボウ株式会社 近赤外線吸収フィルム及び当該フィルムを含む多層パネル
US6731822B1 (en) * 1999-10-28 2004-05-04 Hewlett-Packard Development Company, L.P. Method and apparatus for filtering images having insufficient tonal precision
CN101640753B (zh) * 2009-09-09 2011-03-30 青岛海信移动通信技术股份有限公司 图像处理方法及图像处理装置

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US8184851B2 (en) 1993-11-18 2012-05-22 Digimarc Corporation Inserting watermarks into portions of digital signals
US7992003B2 (en) 1993-11-18 2011-08-02 Digimarc Corporation Methods and systems for inserting watermarks in digital signals
US7945781B1 (en) 1993-11-18 2011-05-17 Digimarc Corporation Method and systems for inserting watermarks in digital signals
US6104377A (en) * 1996-05-24 2000-08-15 Microsoft Corporation Method and system for displaying an image at a desired level of opacity
US6088395A (en) * 1997-09-23 2000-07-11 Winbond Electronics Corp. Compressing/decompressing apparatus and method to compress and decompress a video graphics signal
US7075555B1 (en) * 2000-05-26 2006-07-11 Palmsource, Inc. Method and apparatus for using a color table scheme for displaying information on either color or monochrome display
US6812939B1 (en) 2000-05-26 2004-11-02 Palm Source, Inc. Method and apparatus for an event based, selectable use of color in a user interface display
US20030072468A1 (en) * 2000-12-18 2003-04-17 Digimarc Corporation Curve fitting for synchronizing readers of hidden auxiliary data
US7076082B2 (en) * 2000-12-18 2006-07-11 Digimarc Corporation Media signal filtering for use in digital watermark reading
US6879721B2 (en) 2001-01-02 2005-04-12 Hewlett-Packard Development Company, L.P. Pixel processing system for image production
EP1434195A4 (de) * 2001-09-14 2009-01-21 Nec Corp Bildverarbeitungsvorrichtung, bildübertragungsvorrichtung, bildempfangsvorrichtung und bildverarbeitungsverfahren
CN101162577B (zh) * 2001-09-14 2013-01-23 日本电气株式会社 图像处理装置和方法、图像传送装置和图像接收装置
WO2003025897A1 (fr) * 2001-09-14 2003-03-27 Nec Corporation Appareils de traitement, emission, reception d'images et procede de traitement d'images
US20040252891A1 (en) * 2001-09-14 2004-12-16 Daigo Sasaki Image processing apparatus, image transmission apparatus, image reception apparatus, and image processing method
CN100393100C (zh) * 2001-09-14 2008-06-04 日本电气株式会社 图像处理装置、图像传送装置、图像接收装置和图像处理方法
US7483574B2 (en) * 2001-09-14 2009-01-27 Nec Corporation Image processing apparatus, image transmission apparatus, image reception apparatus, and image processing method
US7231061B2 (en) 2002-01-22 2007-06-12 Digimarc Corporation Adaptive prediction filtering for digital watermarking
US8315427B2 (en) 2002-01-22 2012-11-20 Digimarc Corporation Adaptive prediction filtering for encoding/decoding digital signals in media content
US20030177359A1 (en) * 2002-01-22 2003-09-18 Bradley Brett A. Adaptive prediction filtering for digital watermarking
US7688996B2 (en) 2002-01-22 2010-03-30 Digimarc Corporation Adaptive prediction filtering for digital watermarking
US20100303283A1 (en) * 2002-01-22 2010-12-02 Bradley Brett A Adaptive prediction filtering for encoding/decoding digital signals in media content
US7081901B1 (en) * 2002-08-29 2006-07-25 National Semiconductor Corporation Display system with framestore and stochastic dithering
US7446782B2 (en) 2004-07-07 2008-11-04 Olympus Corporation Image processing device
US20060008155A1 (en) * 2004-07-07 2006-01-12 Takashi Ishikawa Image processing device
US20070279432A1 (en) * 2006-05-31 2007-12-06 Jean Noel Method and Apparatus for Spatial and Temporal Dithering
US7609277B2 (en) * 2006-05-31 2009-10-27 Texas Instruments Incorporated Method and apparatus for spatial and temporal dithering
CN101197118B (zh) * 2006-11-22 2012-01-11 瑞萨电子株式会社 用于改进的frc技术的显示设备和控制驱动器
US20130287101A1 (en) * 2011-10-20 2013-10-31 Thomson Licensing Method and device for encoding a video frame, method and device for decoding a video frame and storage medium
US9621890B2 (en) * 2011-10-20 2017-04-11 Thomson Licensing Method and device for encoding a video frame, method and device for decoding a video frame and storage medium
US20130229425A1 (en) * 2012-03-03 2013-09-05 Mstar Semiconductor, Inc. Image processing method and associated apparatus
US20150117782A1 (en) * 2013-10-31 2015-04-30 Stmicroelectronics Asia Pacific Pte. Ltd. Banding noise detector for digital images
US9183453B2 (en) * 2013-10-31 2015-11-10 Stmicroelectronics Asia Pacific Pte. Ltd. Banding noise detector for digital images

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DE69621208T2 (de) 2002-11-07
DE69621208D1 (de) 2002-06-20
EP0775983B1 (de) 2002-05-15
JPH1026965A (ja) 1998-01-27
EP0775983A2 (de) 1997-05-28
EP0775983A3 (de) 1997-12-29

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